/**
 * (C) Copyright IBM Corp. 2010, 2015
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 */

package com.ibm.bi.dml.runtime.util;

import org.apache.commons.math3.distribution.PoissonDistribution;
import org.apache.commons.math3.random.SynchronizedRandomGenerator;
import org.apache.commons.math3.random.Well1024a;


/**
 * Class that can generate a stream of random numbers from Poisson
 * distribution with specified mean. 
 */


public class PoissonPRNGenerator extends PRNGenerator
{
	PoissonDistribution _pdist = null;
	double _mean = Double.NaN;
	
	private static final double DEFAULT_MEAN = 1.0;
	
	public PoissonPRNGenerator() {
		// default mean and default seed
		super();
		_mean = 1.0;
		setup(_mean, seed);
	}
	
	public PoissonPRNGenerator(double mean) 
	{
		// default seed
		super();
		_mean = mean;
		setup(_mean, seed);
	}
	
	public PoissonPRNGenerator(long sd) {
		// default mean
		super();
		setup(DEFAULT_MEAN, sd);
	}
	
	public void setup(double mean, long sd) {
		seed = sd;
		
		SynchronizedRandomGenerator srg = new SynchronizedRandomGenerator(new Well1024a());
		srg.setSeed(seed);
		_pdist = new PoissonDistribution(srg, _mean, PoissonDistribution.DEFAULT_EPSILON, PoissonDistribution.DEFAULT_MAX_ITERATIONS);
	}
	
	@Override
	public void setSeed(long sd) {
		setup(_mean, sd);
	}
	
	public void setMean(double mean) {
		setup(mean, seed);
	}
	
	public double nextDouble() {
		return (double) _pdist.sample();
	}
	
	

}
